Recently, display elements of image display devices such as a television receiver are undergoing a transition from conventional cathode-ray tubes to thin display devices using thin display elements such as liquid crystal panels and plasma display panels. Such thin display devices enable thinning and weight saving of image display devices. A liquid crystal display device requires a backlight unit as a separate lighting device because the liquid crystal panel is not self-luminous.
Patent Document 1 discloses a backlight unit including: a light guide plate having light entrance surfaces at side surfaces; a light source arranged to be opposed to the light entrance surface of the light guide plate; a light source mount on which the light source is mounted and apart of which is provided between the light source and the light guide plate; and an elastic member abutting the light source mount. In this backlight unit, when the light guide plate expands to the light source side due to heat generated during light emission of the light source, the distance between the light source and the light guide plate is regulated by the light source mount, and the distance between the light guide plate and the light source is kept within a certain range. This maintains the optical design of the backlight unit. Furthermore, the expansion of the light guide plate is absorbed by the elastic member through the light source mount.    Patent Document 1: Japanese Unexamined Patent Publication No. 2002-203418